The Bluetooth system operates in the 2.4 Giga-Hertz (GHz) ISM (Industrial Scientific Medical) band. In the United States, the range of the frequency band is 2.400-2.4835 GHz. The Bluetooth system has channel spacing of 1 MHz and uses 79 radio frequency (RF) channels in its standard hopping sequence. The Federal Communications Commission (FCC) rules mandate that any system that operates under FCC regulation 15.247 must hop over at least 75 RF channels, and must use all the frequencies equally (i.e., the devices must spend the same average amount of time at each frequency). Since Bluetooth was designed to operate under FCC regulation 15.247, its hopping pattern is chosen so that approximately equal time is spent in each of the 79 frequencies. Problems with coexistence can arise when other devices share the ISM band with a Bluetooth system, such as IEEE 802.11b wireless local area networks (WLAN) or microwave ovens.
Interferers, which remain stationary in the ISM band, will greatly reduce the throughput of Bluetooth wireless networks and/or increase the packet error rate (PER) whenever the Bluetooth devices hop into the interfered channels. As an example, a Bluetooth connection carrying a voice conversation generally needs a PER of less than 5%. If a microwave oven is operating near the Bluetooth piconet and occupies a bandwidth of 10 MHz with a 50% duty cycle, then on average 5 RF channels will be unusable to the Bluetooth piconet. The PER floor due to interference from the microwave oven will be about 5/79=6%, which will result in poor voice quality. This invention provides a way to reduce the number of hopping channels so that interferers can be avoided in a frequency hopping system like Bluetooth.